This research is concerned broadly with perception of stimulus structure. The kinds of structure studied are dimensional structure of stimulus sets, distance relations, correlational structure, spatial configuration, and temporal pattern. The research involves three basic approaches: the specification of structure in purely stimulus terms; the perception of that structure as determined by various procedures involving phenomenal description, verbal description, and free classification; and the processing of structure as a form of information, using constrained procedures in which the subject's task is specified and the experimental objective is to determine how well performance is carried out, as indicated by speed and accuracy measures. Some basic concepts behind the research are the information-theoretic concept of information and redundancy, the distinction between state and process in the organism, and the distinction between integral and separable dimensions with respect to dimensional and correlational structure.